The present invention relates to a laser beam luminous energy correction method for correcting the variation caused by a scanning optical system of the luminous energy of a laser beam incident on a scanned surface via the scanning optical system, a laser driving apparatus adopting the laser beam luminous energy correction method, a laser beam scanner for scanning the predetermined scanned surface by a laser beam emitted from a semiconductor laser driven by the laser driving apparatus and incident via the scanning optical system and an image recording device for recording an image using such a laser beam scanner.
Heretofore, for a method of correcting the variation caused by a laser beam scanning optical system of the luminous energy of a laser beam on a scanned surface (the surface of a photoconductor) and the unevenness in density of an image output according to laser xerography, there are first earlier technology (disclosed in the Unexamined Japanese Patent Publication Application No. Sho 53-87747) in which an ND filter for correcting luminous energy distribution is arranged on the optical path of a laser beam, second earlier technology (disclosed in the Examined Japanese Patent Publication Application No. Hei 2-51188) in which correction current based upon a function showing luminous energy distribution is superposed on driving current and makes electric correction, third earlier technology (disclosed in the Unexamined Japanese Patent Publication Application No. Hei 1-182819) in which the gain of a D/A converter is controlled based upon a reference value for controlling luminous energy, fourth earlier technology (disclosed in the Examined Japanese Patent Publication Application No. Hei 5-15339) in which the output of a D/A converter is regulated manually in place of controlling the gain of the D/A converter, fifth earlier technology (disclosed in the Unexamined Japanese Patent Publication Application No. Hei 1-302367) in which the maximum luminous energy and the minimum luminous energy are respectively regulated to the maximum driving current and the minimum driving current and the difference is linearly corrected and others.
However, there is a problem in the first earlier technology using the above ND filter that as the cost of the ND filter itself is high and in addition, the distribution of luminous energy varies according to the design of an optical system, the ND filter is required to be remodeled every time. There are also various problems in an electric correction method heretofore proposed as explained below.
FIG. 37 is a circuit diagram showing the above second earlier technology. An added value is acquired by adding a function value generated in a function signal generator 331 and according to a scanned position and a reference value from a reference signal circuit 332 by an adder 333 so as to use the added value for the reference value of current for driving a laser.
There is a problem that as in this method, a function value is added to the reference value using the adder 333, a function is required to be reset every time the characteristics of a laser vary because of the environmental change of temperature, humidity and others, aging change and others and this method cannot correspond to the change of the characteristics of the laser.
In the above circuit, current flowing to a laser 334 is detected and led to a comparator 335, however, there is a problem related to not current flowing in the laser 334 but the luminous energy of a laser beam emitted from the laser 334 and the variation caused by the change of the characteristics of the laser 334 of the luminous energy of a laser beam for current flowing in the laser 334 cannot be corrected.
FIG. 38 is a circuit diagram showing the above third earlier technology. Reference voltage Vref acquired by a reference voltage generator 341 and a voltage value showing the emission luminous energy of a laser 343 and detected by an optical detector 342 are compared by a comparator 344, a count value showing laser emission luminous energy according to the reference voltage Vref is acquired in an updown counter 348 by transmitting the result of the comparison to the updown counter 348, the count value is converted to an analog signal by a D/A converter 346 and transmitted to a computing element 347. In the meantime, a digital value according to a signal showing a scanned position acquired by an image scanning clock generator 349 is output from a digital value setting circuit 353, the digital value is converted to an analog signal by a D/A converter 350 and input to the computing element 347. The computing element 347 applies predetermined operation to two analog signals respectively transmitted from the two D/A converters 346 and 350 and transmits the result of the operation to a semiconductor laser driving circuit 351. Gain control based upon reference voltage Vref is applied to the D/A converter 350 by a gain control section 352. That is, a correction coefficient every scanned position is generated in the digital value setting circuit 348 and the correction coefficient is multiplied by a coefficient varying according to reference voltage Vref in automatic luminous energy control so as to suppress the a variation of luminous energy on a scanned surface.
However, in the above Examined Japanese Patent Publication Application No. Hei 2-51188, it is not described that any current component of current supplied to a semiconductor laser is to be corrected and there is a problem that a method of controlling the gain of the D/A converter 350 by the gain control section 352 is required to be changed every time the characteristic of a laser varies and the third earlier technology cannot correspond to the change of the characteristic of a laser as in the earlier technology described referring to FIG. 37.
In the above fourth earlier technology, an amplifier for controlling the output of the D/A converter 350 manually in provided in place of the gain control section 352 shown in FIG. 38 and as manual control is executed in this case, manual control is naturally executed every time the characteristic of a laser varies.
Further, in the Examined Japanese Patent Publication Application No. Hei 4-750702, the technique of controlling the emission luminous energy of a laser beam by controlling bias current is disclosed, however, the above technique also has a problem that is cannot correspond to the change of the characteristic of a laser.
As the above fifth earlier technology respectively relates the maximum luminous energy and the minimum luminous energy to the maximum driving current and the minimum driving current and linearly corrects the difference, the problems in the second and third earlier technologies are solved. However, if the fifth earlier technology is applied to laser xerography, the maximum luminous energy and the minimum luminous energy are required to be regulated due to ambient temperature and humidity or the deterioration of a photoconductor, however, reference voltage for the maximum and minimum luminous energy is fixed and it is not considered that if the maximum and minimum luminous energy is not controlled holding proportional relationship between the maximum luminous energy and the minimum luminous energy, laser beam luminous energy is not corrected right. The fifth earlier technology adopts a method that relationship between a correction value acquired by a correction coefficient circuit and the actual variation of laser beam luminous energy is defined by controlling luminous energy based upon two reference values Vp and Vb. As a result, though automatic luminous energy control is required only once if on-off control is executed by fixed luminous energy as in prior pulse length modulation, the above control is required to be executed twice in the case of the fifth earlier technology. In laser xerography, as automatic luminous energy control is required twice and effective time in which modulation by a picture signal is enabled is reduced when time required for luminous energy control is extended, countermeasures such as increasing the frequency of a clock and extending distance scanned by a laser beam are required to secure the same print speed and the cost is increased. Further, if intensity modulation described below is executed together, luminous energy control is required twice every level. As in a digital circuit, luminous energy control is originally executed by software, luminous energy control takes long time and if luminous energy control in short time at the beginning of each scan (each vertical scanning) as analog automatic luminous energy control is tried, only luminous energy control in units of page is enabled. Therefore, in laser xerography in which the high reproducibility of gradation is required, digital automatic luminous energy control in short time is difficult, however, if automatic luminous energy control is required twice, it is further difficult. If the fifth earlier technology is applied as a correction method when intensity modulation is executed using plural current sources as disclosed in the Unexamined Japanese Patent Publication Application No. Sho 63-184773, a problem that the correction factor of laser beam luminous energy varies depending upon a level of intensity modulation occurs because threshold current at an extrapolated point is not considered.
The Unexamined Japanese Patent Publication Application No. Hei 4-263566 shows countermeasures against automatic luminous energy control being required twice which is a problem of a fifth earlier technology and for intensity modulation using plural current source. According to technique disclosed in the above application, current in a laser oscillation area slightly larger than the threshold current of a laser is used, desired luminous energy is emitted based upon current on which a value acquired by multiplying the current by a correction coefficient is superposed, and another current source is set off against an error caused because current larger than threshold current at an extrapolated point is set. In the case of technique disclosed in the above application, as a circuit is complicated and in addition, current exceeding laser oscillation threshold current is regularly applied, there is a problem that an image is fogged overall in case the above technique is applied to laser xerography, and the above technique has a problem that as a method of calculating xcex8xc2x7K (xcex8: emission efficiency, K: gain for converting image data to current) of conditions shown in the above application for a current value in an addition circuit to be set is not shown, xcex8xc2x7K is required to be acquired based upon laser beam luminous energy and laser driving current at two points as in the fifth earlier technology. Therefore, as a result, the problems in the fifth earlier technology are not solved. Further, the object of the technique disclosed in the above Unexamined Japanese Patent Publication Application No. Hei 4-263566 is to correct the equivalent variation of luminous energy (density) caused by the ununiformity of the rotation of a scanned object in the shape of a rotary roll and the object is not to correct the variation of luminous energy caused by a scanning optical system and the dispersion of the surface of a photoconductor respectively in question. In the Unexamined Japanese Patent Publication Application No. Hei 5-19599, technique for correcting the equivalent variation of luminous energy (density) caused by the ununiformity of the rotation of a scanned object in the shape of a rotary roll is also disclosed.
In the Unexamined Japanese Patent Publication Application No. Hei 9-197316, bias current is set so that it has a lower value than threshold current and a problem that an image is fogged is not caused in laser xerography. As a current indicated value Ipth corresponding to reference luminous energy Pth is a slightly larger value than a threshold at which the oscillation of a laser is started as disclosed in the above application and is not threshold current at an extrapolated point, the above current indicated value includes an error of correction. As the above method includes no circuit to correct difference from a threshold at an extrapolated point differently from the technique disclosed in the above Unexamined Japanese Patent Publication Application No. Hei 4-263566, correction quantity is different depending upon an output level. If Ipth can be reduced so that it has minute luminous energy when it is defined, the above difference can be also reduced, however, depending upon a method of connecting a PIN photodiode which receives the back radiation of a laser, if the output of a light receiving element is sink current, it is once converted to source current, current-voltage conversion is required to be executed in a resistor one end of which is grounded, and if luminous energy is minute and current equivalent to a received beam is small in case a current mirror circuit used for the above sink-source conversion is used, the input impedance of the current mirror circuit is increased and a frequency characteristic is greatly deteriorated. As a result, the time of automatic luminous energy control is greatly extended and in the worst case, a phenomenon of oscillation is caused depending upon a control method. As the oscillation mode of a laser is different from the mode of image modulation and spontaneous emission is included if luminous energy is minute, there is also a problem that driving current for laser oscillation to the output of a laser beam is not linear. Further, as in a semiconductor laser, a threshold is varied depending upon temperature, the smallest value of laser beam luminous energy at which a laser beam can be stably used is equivalent to approximately a few to 10% of the maximum rating luminous energy. Therefore, for example, if luminous energy on an actual printing condition is set so that it is equivalent to 50% and 30% of the maximum rating after Ipth is set so that it is equivalent to 10% of the maximum rating and a correction coefficient is calculated so that a beam has the maximum luminous energy, correction values are respectively equivalent to 82.2% and 85.2% for the setting equivalent to 80% as to an error of luminous energy. Further, if intensity modulation is executed and intensity is set to ⅓, correction values are respectively equivalent to 91.1% and 100% for the setting equivalent to 80% and in the worst case, a correction value is equivalent to 100% for the setting equivalent to 80% and an error of 20% is made. (Refer to FIGS. 6 and 7 described later and the explanation.) As the precision of approximately 0.4% is required to acquire the true reproducibility of 256 gradations, only luminous energy in the vicinity where a correction coefficient is calculated is used and as a result, reference luminous energy is automatic luminous energy control cannot be actually regulated according to output density in laser xerography.
The object of the present invention is to provide a laser beam luminous energy correction method, a laser driving apparatus, a laser beam scanner and an image recording device wherein the variation of the luminous energy caused by a scanning optical system of a laser beam scanned on a scanned surface via a vertical scanning optical system can be precisely corrected in view of the above conditions.
A first aspect of the present invention (an invention according to claim 1) is based upon a laser luminous energy correction method for correcting the variation of an output beam according to a beam position or an angle of incidence with a scanned surface when a beam output from a laser is scanned on the scanned surface via a scanning optical system to solve the above problems and characterized in that a current value exceeding a threshold current part having a current value in the vicinity in a spontaneous emission area of an extrapolated point which is an intersection with an axis when a linear part corresponding to a laser emission area in the driving current-to-output beam luminous energy characteristic of a laser is extrapolated up to the axis showing that luminous energy is zero is corrected using a correction value for correcting the variation of an output beam according to an angle of incidence with a scanned surface and the above laser is driven based upon the result of the correction and the above threshold current.
According to the first aspect, as a current value exceeding the threshold current part having a current value in the vicinity in the spontaneous emission area of the extrapolated point is corrected as described above, the variation of an output beam according to a beam position or an angle of incidence with the scanned surface can be precisely corrected. That is, the closer to a current value at the extrapolated point which is an ideal current value the current value of threshold current is, the more precisely threshold current can be corrected.
A second aspect (an invention according to claim 2) is based upon a laser driving apparatus for driving a laser (110) the output beam of which is scanned on a scanned surface via a scanning optical system and characterized in that generation means (18) for generating a correction value for correcting the variation of output according to an angle of incidence with a scanned surface, multiplication means (17) for multiplying a reference value by the correction value from the above generation means, first generation means (13) for including a constant current source the current value of which is controlled based upon the result of the multiplication by the multiplication means and generating modulation current (Is2) acquired by modulating current flowing in the constant current source according to image data, second generation means (12, 11) for generating threshold current (Is1+Ib) having a current value in the vicinity in a spontaneous emission area of an extrapolated point which is an intersection with an axis when a linear part corresponding to a laser emission area in the driving current-to-output beam luminous energy characteristic of a laser is extrapolated up to the axis showing that luminous energy is zero and addition means (10) for driving the laser based upon current generated from first and second current sources are provided.
According to the second aspect, the current value of the constant current source is controlled based upon the result of the multiplication of the reference value and the correction value by the multiplication means, the first generation means generates modulation current acquired by modulating current the current value of which is controlled according to image data and the second generation means generates threshold current having a current value in the vicinity in the spontaneous emission area of the extrapolated point. The above modulation current and threshold current are added (superposed) by the addition means and the laser is driven. As a result, as a current area exceeding threshold current is corrected, the variation of an output beam according to a beam position or an angle of incidence with the scanned surface can be precisely corrected. As the reference value is multiplied by the correction value, a correction value is not required to be varied even if intensity is required to be varied because of the condition of the scanning optical system and the scanned surface. Further, as the current value of the constant current source is controlled based upon the result of the multiplication, a correcting circuit can be realized by simple configuration.
A third aspect (an invention according to claim 3) is based upon a laser driving apparatus for driving a laser (100) the output beam of which is scanned on a scanned surface via a scanning optical system and characterized in that first generation means (18) for generating a correction value for correcting the variation of an output beam according to a beam position or an angle of incidence with a scanned surface, multiplication means (17) for multiplying a reference value by the correction value from the generation means, second generation means (13) for including one or more constant current sources the current value of which is controlled based upon the result of the multiplication by the multiplication means, selecting any of the constant current sources according to input image data and generating modulation current (Is2) acquired by modulating current flowing in the selected constant current source according to the image data, second current sources (12, 11) for generating threshold current (Is1+Ib) having a current value in the vicinity in a spontaneous emission area of an extrapolated point which is an intersection with an axis when a linear part corresponding to a laser emission area in the driving current-to-output beam luminous energy characteristic of a laser is extrapolated up to the axis showing that luminous energy is zero and addition means (10) for driving the laser based upon current generated from the second generation means and the second current source are provided.
According to the third aspect, the current value of one or more constant current sources is controlled based upon the result of the multiplication of the reference value and the correction value by the multiplication means, the first generation means selects the constant current source the current value of which is controlled according to image data and generates modulation current acquired by modulating current flowing in the selected constant current source according to the image data, and the second generation means generates threshold current having a current value in the vicinity in the spontaneous emission area of the extrapolated point. The modulation current and the threshold current are added by the addition means and the laser is driven. As a result, as current in the current area exceeding the threshold current is corrected, the variation of an output beam according to an angle of incidence with the scanned surface can be precisely corrected. As correction that the reference value is multiplied by the correction value is made, the correction value is not required to be varied even if intensity modulation according to image data is executed and intensity is required to be varied according to the condition of the scanning optical system and the scanned surface. Further, as the current value of the constant current source is controlled based upon the result of the multiplication, a correcting circuit can be realized by simple configuration.
As for the second and third aspects, it is desirable that the above second generation means includes third generation means (11) for generating bias current (Ib) regularly output independent of when image data is input and fourth generation means (12) for generating current (Is1) output when image data showing the emission of a laser beam is input and that the above threshold current is generated based upon current output from the third and fourth generation means. As a result, as bias current is also supplied when a laser beam is not emitted, the laser can be driven at high speed.
A fourth aspect (an invention according to claim 6) is based upon a laser driving apparatus for generating supply current modulated according to image data and driving a semiconductor laser for emitting a laser beam having luminous energy according to the supply current and scanned on a scanned surface via a scanning optical system by the supply current and characterized in that a modulation current source (51) to which a predetermined gain control signal and image data are input for outputting modulation current which composes a part of supply current, by which the image data is converted so that it has gain according to the gain control signal and which is modulated according to the image data, threshold current sources (52_1, 52_2) for outputting threshold current according to a predetermined current control signal which composes the above supply current together with the above modulation current and a computing element (53) for generating the above gain control signal by multiplying a gain set value which functions as the criterion of the gain of the modulation current source (51) by a correction value according to a beam position or an angle of incidence with a scanned surface varying according to scanning of a laser beam emitted from a semiconductor laser (100) and generating a current control signal to control so that threshold current output from the threshold current sources (52_1, 52_2) has a current value in the vicinity in a spontaneous emission area of an extrapolated point which is an intersection with an axis when a linear part corresponding to a laser emission area in the supply current-to-output beam luminous energy characteristic of the semiconductor laser is extrapolated up to the axis showing that luminous energy is zero are provided.
According to the fourth aspect, as the modulation current source (51) and the threshold current sources (52_1, 52_2) are provided and further, the computing element (53) for generating a gain control signal for controlling the modulation current source by multiplying the gain set value by the correction value and generating a current control signal for controlling so that threshold current in the threshold current source has a current value in the vicinity in the spontaneous emission area of the extrapolated point are provided, threshold current is regulated right, a modulation current part exceeding the threshold current is corrected and therefore, the variation of an output beam according to an angle of incidence with the scanned surface can be precisely corrected. As correction that the reference value is multiplied by the correction value is made, the correction value is not required to be varied even if intensity is required to be varied according to the condition of the scanning optical system and the scanned surface. Further, as the current value of the constant current source is controlled based upon the result of the multiplication, a correcting circuit can be realized by simple configuration.
Further, a fifth aspect (an invention according to claim 8) is based upon a laser driving apparatus for generating supply current modulated according to image data and driving a semiconductor laser for emitting a laser beam having luminous energy according to the supply current and scanned on a scanned surface via a scanning optical system by the supply current and characterized in that a modulating current source (91) to which a predetermined gain control value and image data are input for outputting modulation current which composes a part of the above supply current, by which the image data is converted so that it has gain according to the gain control value and which is modulated according to the image data, gain correction means (98) for generating the above gain control value by multiplying a gain set value which functions as the criterion of the gain of the modulation current source by a correction coefficient according to an angle of incidence with a scanned surface varying according to scanning of a laser beam emitted from a semiconductor laser and transmitting the gain control value to the modulation current source (91), threshold current sources (92_1, 92_2) for generating threshold current according to a current control value, monitor value generation means (93) for generating a monitor value acquired by adding a first monitor value acquired by converting a predetermined set value so that it has gain according to the above gain control value and a second monitor value according to the above current control value, current control value generation means (94) to which emission luminous energy monitor signal acquired by monitoring the emission luminous energy of a semiconductor laser (100) and a predetermined first reference value are input for generating the above current control value so that the semiconductor laser emits with emission luminous energy corresponding to the first reference value, gain set value generation means (95) to which the monitor value generated by the monitor value generation means (93) and a predetermined second reference value are input for generating a gain set value so that a monitor value corresponding to the second reference value is generated by the monitor value generation means (93), first sample-hold means (96) which can be switched to a through state in which input is output as it is and a hold state in which a value the input of which is sample-held is output for supplying a current control value generated by the current control value generation means (94) to the bias current source and a monitor value generation circuit as it is in the through state and with the current control value held in the hold state and second sample-hold means (97) which can be switched to a through state in which input is output as it is and a hold state in which a value the input of which is sample-held is output for supplying a gain set value generated by the gain set value generation means (95) to the gain correction means (98) and the monitor value generation means (93) as it is in the through state and with the gain set value held in the hold state are provided, and a first mode for keeping the above first and second sample-hold means (96, 97) in a through state and regulating the above gain set value and the above current control value using a correction value fixed in the gain correction means (98) and a second mode for keeping the first and second sample-hold means (96, 97) in a hold state, generating the above gain control value in the gain correction means (98) using the correction value according to an angle of incidence and outputting driving current in a driving current source by which image data is converted so that it has gain according to a gain control value and which is modulated according to the image data are provided.
According to the fifth aspect, in the above first mode, the first and second sample-hold means (96, 97) are kept in a through state, the current control value generation means (94) and the gain set value generation means (95) are operated, threshold current is set to a threshold at an extrapolated point and a gain set value which functions as a criterion for correcting modulation current in a modulation current part exceeding threshold current is acquired. As described above, according to the fifth aspect, the threshold at the extrapolated point and the gain set value can be acquired at high speed by analog operation. Afterward, as the control is switched to open-loop control, threshold current is fixed, the gain set value is multiplied by a correction value by the gain correction means (98) and modulation current in a modulation current part exceeding threshold current is precisely corrected when the first mode is switched to the second mode, the similar action to that in the laser driving apparatus according to the above present invention is produced and the variation of an output beam according to a beam position or an angle of incidence with the scanned surface can be precisely corrected.
A sixth aspect (an invention according to claim 10) is based upon a laser beam scanner for scanning a predetermined scanned surface by a laser beam holding image information and characterized in that a semiconductor laser (1122) for emitting a laser beam having luminous energy according to supply current, a laser driving circuit (1121) for generating supply current modulated according to image data and driving the semiconductor laser by the supply current and scanning optical systems (1123, 1124, 1125) for scanning a laser beam emitted for the semiconductor laser on a predetermined scanned surface are provided, the above laser driving circuit (1121) includes generation means (18) for generating a correction value for correcting the variation of an output beam according to an angle of incidence with the above scanned surface, multiplication means (17) for multiplying a reference value by the correction value from the generation means and a constant current source the current value of which is controlled based upon the result of the multiplication by the multiplication means and is provided with first generation means (13) for generating modulation current (Is2) acquired by modulating current flowing in the constant current source according to the image data, second generation means (12, 11) for generating threshold current (Is1+Ib) having a current value in the vicinity in a spontaneous emission area of an extrapolated point which is an intersection with an axis when a linear part corresponding to a laser emission area in the modulation current-to-output beam luminous energy characteristic of the laser is extrapolated up to the axis showing that luminous energy is zero and addition means (10) for driving the laser based upon current generated from the first and second current sources.
The sixth aspect relates to the laser beam scanner for generating a laser beam holding image information using the laser driving apparatus according to the present invention and scanning the scanned surface by the laser beam, the variation due to the laser beam scanning optical system of luminous energy can be precisely corrected and a laser beam actually holding image information can be scanned.
Further, a seventh aspect (an invention according to claim 11) is based upon an image recording device utilizing a process for scanning a predetermined scanned surface by a laser beam holding image information in a process for recording an image and characterized in that a semiconductor laser for emitting a laser beam having luminous energy according to supply current, a laser driving circuit for generating supply current modulated according to image data and driving the semiconductor laser by the supply current and a scanning optical system for scanning a laser beam emitted from the semiconductor laser on the predetermined scanned surface are provided, and the above laser driving circuit is provided with generation means (18) for generating a correction value for correcting the variation of an output beam according to a beam position or an angle of incidence with the scanned surface, multiplication means (17) for multiplying a reference value by the correction value from the above generation means, first generation means (13) for including a constant current source the current value of which is controlled based upon the result of the multiplication by the above multiplication means and generating modulation current (Is2) acquired by modulating current flowing in the constant current source according to the above image data, second generation means ((12, 11) for generating threshold current (Is1+Ib) having a current value in the vicinity in a spontaneous emission area of an extrapolated point which is an intersection with an axis when a linear part corresponding to a laser emission area in the modulation current-to-output beam luminous energy characteristic of the laser is extrapolated up to the axis showing that luminous energy is zero and addition means (10) for driving the laser based upon current generated from the first and second current sources.
The seventh aspect relates to the image formation device for generating a laser beam holding image information using the laser driving apparatus according to the present invention and finally forming an image by scanning the scanned surface by the laser beam and according to the seventh aspect, the variation of luminous energy caused by the laser scanning optical system is precisely corrected and a high quality of image having precise density can be formed. As configuration for multiplying a correction value is provided, the above variation can be readily corrected by having a correction value according to repeatedly caused unevenness such as unevenness in sensitivity, electrification and transfer.
An eighth aspect (an invention according to claim 13) is based upon a laser driving method for driving a laser of which the output beam is scanned on a scanned surface via a scanning optical system,
the laser driving method comprising the steps of:
generating a correction value for correcting the variation of an output beam according to a beam position or an angle of incidence with the scanned surface;
multiplying a reference value by the correction value obtained by the generation step;
with a constant current source in which a current value is controlled based upon the result of the multiplication obtained by the multiplication step, first generating for generating modulation current acquired by modulating current flowing in the constant current source according to the image data;
second generating for generating threshold current having a current value in the vicinity in a spontaneous emission area of an extrapolated point which is an intersection with an axis when a linear part corresponding to a laser emission area in the driving current-to-output beam luminous energy characteristic of the laser is extrapolated up to the axis showing that luminous energy is zero; and
addition for driving a laser based upon current generated from the first and second current generating steps.
A ninth aspect (an invention according to claim 14) is based upon a laser driving method for driving a laser of which the output beam is scanned on a second surface via a scanning optical system, comprising the steps of:
first generating for generating a correction value for correcting the variation of an output beam according to a beam position or an angle of incidence with the scanned surface;
multiplying a reference value by the correction value obtained by the first generation step;
with one or more constant current sources in which a current value is controlled based upon the result of the multiplication obtained by the multiplying step, second generating for selecting the constant current source according to input image data and for generating modulation current acquired by modulating current flowing in the selected constant current source according to the image data;
generating threshold current having a current value in the vicinity in a spontaneous emission area of an extrapolated point which is an intersection with an axis when a linear part corresponding to a laser beam emission area in the driving current-to-output beam luminous energy characteristic of the laser is extrapolated up to the axis showing that luminous energy is zero by a second current source; and
addition for driving a laser based upon current generated from the second generation step and the second current step.
The tenth aspect relates to the laser driving method according to the eighth or ninth aspect, wherein:
the second generation step comprises:
third generation step for generating bias current regularly output independent of time when the image data is input, and
fourth generation step for generating current output when the image data is input meaning the emission of the laser; wherein
the threshold current is generated based upon current output from the third and fourth generation means.
An eleventh aspect (according to claim 17) is based upon a laser driving method for generating supply current modulated according to image data and driving a semiconductor laser for emitting a laser beam having luminous energy according to supply current by the supply current for scanning a scanned surface via a scanning optical system,
the laser driving method comprising the steps of:
modulation in which a predetermined gain control signal and image data are input for outputting modulation current which composes a part of the supply current, by which the image data is converted so that it has gain according to the gain control signal and which is modulated according to the image data;
outputting threshold current included in the modulation current and the supply current according to a predetermined current control signal; and
generating the gain control signal by multiplying a gain set value which functions as the criterion of the gain of the modulation step by a correction value according to a beam position or an angle of incidence varying according to scanning with the scanned surface of a laser beam emitted from the semiconductor laser, and
generating the current control signal to control so that threshold current output from the threshold current source is a current value in the vicinity in a spontaneous emission area of an extrapolated point which is an intersection with an axis when a linear part corresponding to a laser emission area in the supply current-to-output beam luminous energy characteristic of the semiconductor laser is extrapolated up to the axis showing that luminous energy is zero.
A twelfth aspect (according to claim 18) is based upon a laser driving method according to the eleventh aspect, wherein:
the generating the current control signal step comprises:
inputting a monitoring signal for monitoring the luminous energy of a laser beam emitted from the semiconductor laser for acquiring emission efficiency represented by the inclination of the linear part,
generating the gain set value based upon the emission efficiency,
acquiring an extrapolated point according to the monitoring signal, and
generating the current control signal based upon the extrapolated point.
A thirteenth aspect (an invention according to claim 19) is based upon a laser driving method for generating supply current modulated according to image data and driving a semiconductor laser for emitting a laser beam having luminous energy according to the supply current for scanning a scanned surface via a scanning optical system by the supply current,
the laser driving method comprising the steps of:
outputting modulation current which composes a part of the supply current by a modulation current source to which a predetermined gain control value and image data are input, by which the image data is converted so that it has gain according to the gain control value and which is modulated according to the image data;
generating the gain control value by gain correction means by multiplying a gain set value which functions as the criterion of the gain of the modulation current source by a correction value according to a beam position or an angle of incidence varying according to scanning with the scanned surface of a laser beam emitted from the semiconductor laser and transmitting the gain control value to the modulation current source by gain correction means;
generating threshold current by a threshold current source according to a current control value and composing the modulation current and the supply current;
generating a monitor value by monitor value generation means by adding a first monitor value to which a predetermined set value is converted so that it has gain according to the gain control value and a second monitor value according to the current control value;
generating the current control value by current control value generation means to which an emission luminous energy monitoring signal for monitoring the emission luminous energy of the semiconductor laser and a predetermined first reference value are input so that the semiconductor laser emits a beam having emission luminous energy corresponding to the first reference value;
generating the gain set value so that a monitor value corresponding to the second reference value is generated by the monitor value generation means by gain set value generation means to which a monitor value generated by the monitor value generation means and a predetermined second reference value are input;
supplying a current control value generated by the current control value generation means as it is in the through state and with the current control value held in the hold state to the bias current source and the monitor value generation means, by first sample-hold means capable to be switched to a through state in which input is output as it is and to a hold state in which a value the input of which is sample-held is output; and
supplying a gain set value generated by the gain set value generation means as it is in the through state and with the gain set value held in the hold state to the gain correction means and the monitor value generation means, by second sample-hold means capable to switched to a through state in which input is output as it is and to a hold state in which a value the input of which is sample-held is output, wherein
the laser driving apparatus utilizes:
a first mode for keeping the first and second sample-hold means through and controlling the gain set value and the current control value using a correction value fixed in the gain correction means; and
a second mode for keeping the first and second sample-hold means sample-held, generating the gain control value using a correction value according to the angle of incidence in the gain correction means and outputting driving current by which image data is converted so that the image data has gain according to the gain control value in the driving current source and which is modulated according to the image data.
A fourteenth aspect (an invention according to claim 20) is based upon a laser driving method according to the thirteenth aspect, further comprising:
a low-pass filter located between the gain correction means and the modulation current source, and operated in the second mode.
A fifteenth aspect (an invention according to claim 21) is based upon a laser beam scanning method for scanning a predetermined scanned surface by a laser beam holding image information,
the laser beam scanning method comprising the steps of:
emitting a laser beam having luminous energy according to supply current by a semiconductor laser;
generating supply current modulated according to image data and driving the semiconductor laser by the supply current by a laser driving circuit; and
scanning the predetermined scanned surface by a scanning optical system for helping a laser beam emitted from the semiconductor laser, wherein:
the semiconductor laser driving method comprises the steps of:
generating a correction value for correcting the variation of an output beam according to an angle of incidence with the scanned surface by generation means;
multiplying a reference value by a correction value from the generation means by multiplication means;
generating modulation current acquired by modulating current flowing in the constant current source according to the image data by first generation means with a constant current source the current value of which is controlled based upon the result of the multiplication by the multiplication means, by the first generation means;
generating threshold current having a current value in the vicinity in a spontaneous emission area of an extrapolated point which is an intersection with an axis when a linear part corresponding to a laser emission area in the driving current-to-output beam luminous energy characteristic of the laser is extrapolated up to the axis showing that luminous energy is zero, by second generation means; and
driving a laser based upon current generated from the first and second current sources by addition means.
A sixteenth aspect (an invention according to claim 22) is based upon a laser beam scanning method according to the fifteenth aspect, wherein:
the scanning optical system comprises:
a rotating polygon mirror for reflecting and deflecting a laser beam emitted from the semiconductor laser, and
a beam diameter control optical member for regulating a laser beam emitted from the semiconductor laser and outgoing from one mirror surface of the rotating polygon mirror so that the beam has a predetermined beam diameter, and leading the beam to the rotating polygon mirror.
A seventeenth aspect (an invention according to claim 23) is based upon an image recording method with a process for scanning a predetermined scanned surface by a laser beam holding image information in a process for recording an image,
the image recording method comprising the steps of:
causing a semiconductor laser beam having luminous energy according to supply current emit;
causing a laser driving circuit generate supply current modulated according to image data and driving the semiconductor laser by the supply current; and
causing scanning optical system for helping a laser beam emitted from the semiconductor laser scan a predetermined scanned surface, wherein:
the step of causing the laser driving circuit generate supply current comprises:
generating a correction value for correcting the variation of an output beam according to a beam position or an angle of incidence with the scanned surface by generation means;
multiplying a reference value by a correction value from the generation means by multiplication means;
generating modulation current acquired by modulating current flowing in the constant current source according to the image data, by first generation means with a constant current source the current value of which is controlled based upon the result of the multiplication by the multiplication means;
generating threshold current having a current value in the vicinity in a spontaneous emission area of an extrapolated point which is an intersection with an axis when a linear part corresponding to a laser emission area in the driving current-to-output beam luminous energy characteristic of the laser is extrapolated up to the axis showing that luminous energy is zero by second generation means; and
driving a laser based upon current generated from the first and second current sources by addition means.